There are what are known as the plastic infusion containers; a bag type made of a plastic sheet and a bottle type produced by blow-molding.
The bottle type infusion containers have the advantage of being able to stand upright. However, such bottle type infusion containers are formed by blow-molding, causing problems in flexibility. Thus, the blow-molded containers can not be sufficiently flattened under pressure by the discharge of the drug solution, causing excessive amounts of the drug solution to remain in the container. For this reason, some measures taken in the prior art are those such as, for example, a method of inserting an air needle into a rubber stopper of the container, in which the inside and the outside of the container are fluid-communicated with each other through said air needle to allow the air to flow into the container in response to the outflow of the drug solution when performing the transfusion of the drug solution at a constant flow rate, or use of an infusion container filled with the drug solution of less than the container capacity to increase an amount of air or gas to be contained in the container.
However, the method of insertion of the air needle into the rubber stopper of the container has a disadvantage for working since it takes a lot of trouble for insertion of the air needle and since it requires extreme care to prevent it from being contaminated by harmful bacteria. Further, the method of increasing the content of the gas such as air in the container is disadvantageous in that the container increases in size with reserving the space for air to be charged therein. In addition, the method, when performed by the use of an infusion pump, necessitates additional human hands and devices since it is necessary to monitor and prevent the introduction of excess air into the blood vessel of the patient because of a fluid level sensor failure.
On the other hand, the bag type containers have the advantage of being able to exclude the residual liquid from the container since all parts except the mouth of the container are made of a flexible plastic sheet and thus they are easily flattened by themselves in response to the outflow of the drug solution without use of any air needle. However, such bag type containers have a disadvantage for performing the infusion since they can not be held upright because of the material and shape of the container.
As a result, there have been proposed bottle type infusion containers capable of being kept upright, which are adapted to be easily flattened to reduce the air quantity and residual liquid, such as an infusion container provided with four grooves parallel to the bottom in places in wide sidewalls of the barrel (patent document 1), and an infusion container provided with mountain fold lines (5, 5) passing longitudinally through the center of both sidewalls of the container barrel, said mountain fold lines bifurcating at the position near the bottom and extending from said position to both corners of sidewalls near the bottom, wherein the barrel is further provided with valley fold lines (5a, 5a) on both sides of each mountain fold line (5, 5), and a valley fold line (7) passing through the side walls and a front wall of the container barrel in parallel with the bottom to communicate the valley fold lines with each other (patent document 2).
However, the infusion container of patent document 1 possesses insufficient flattening of the shoulder and bottom, and thus there is dissatisfaction with a large amount of air to be injected. The infusion container of patent document 2 has been somewhat improved in flattening property, but it is insufficient in flattening of the shoulder and bottom, in particular, flattening of the shoulder, which therefore causes dissatisfaction because of a large amount of air to be injected.    Patent document 1: JP, H06-000114Y    Patent document 2: JP, P2002-282335A